Typically, optical disc players such as LDPs, CDPs, CD-ROM and DVD-ROM players, DVD players, and BD and 3D players, are apparatuses including operations of: loading a disc onto a turntable by a loading mechanism; clamping, fitting and fixing a mounting hole formed at the center of the disc with a chuck that is a clamping unit; rotating the disc clamped in the chuck in one direction by a drive source of a spindle motor drive unit; and reproducing information recorded on the disc by an optical pickup unit that moves in a radial direction of the disc.
In general, the spindle motor maintains a constant contact section between the bearing and the rotating shaft, to thereby rotatably support the rotating shaft and to thus maintain high accuracy rotational characteristics, with a result of being widely employed as a driving unit for driving a hard disc drive (HDD), optical disc drive (ODD) and other recording media requiring high-speed rotation.
The spindle motor requiring high-speed rotation becomes thinner and lighter to meet development of ever-smaller electronic devices, and an example of the spindle motor is schematically shown in FIG. 1 (see Korean Laid-open Patent Publication No. 10-2010-0043525).
FIG. 1 is a cross-sectional view of a conventional spindle motor. As shown, the conventional spindle motor is combined by inserting an outer circumferential surface of the lower end of a bearing housing 13 into a coupling hole formed in a base plate 11 to thus spinning or caulking an outer projection 13a. Slit washers 14 and a cap 15 are coupled on an inner circumferential surface of the lower end of the bearing housing 13, in order to prevent a rotating shaft 19 from seceding, in which the cap 15 is combined by spinning or caulking an inner projection 13b of the lower end of the bearing housing 13.
A sleeve bearing 17 is fixed in the bearing housing 13 and the rotating shaft 19 is supported by the sleeve bearing 17, in which the rotating shaft 19 is rotatably supported by the sleeve bearing 17. A support washer 16 that is provided in the lower end of the rotating shaft 19 to reduce a rotational resistance of the rotating shaft 19 is disposed in the cap 15.
In this case, the sleeve bearing 17 is sintered to thus be formed of a porous material having a large number of pores therein. Here, oil is leaked from the pores during rotation of the rotating shaft 19 by impregnating the pores with oil. Accordingly, an oil film is formed between the bearing sleeve 17 and the rotating shaft 19, to thus minimize the friction therebetween.
The oil is circulated along a path of rising up along between the sleeve bearings 17 and the rotating shaft 19, and then falling down along four recesses 17a (see FIG. 2) that are formed on the outer circumference of the sleeve bearing 17 through an oil shatter-proof washer 20 for preventing oil from scattering.
In addition, a stator 21 having a core 21a and a coil 21b is fixed on the outer circumferential surface of the bearing housing 13, and a rotor 23 having a rotor yoke 23a and a magnet 23b is fixed on the leading end of the rotating shaft 19.
The upper surface of the rotor yoke 23a of the rotor 23 plays a role of a turntable on which a disc D storing data is secured and seated. To this end, a rubber ring 12 is arranged on the outside of the upper surface of the rotor yoke 23a to thus prevent the disc D from slitting, and a chucking device 18 having a disc chuck 18b and a chuck case 18a is provided on the inside of the upper surface of the rotor yoke 23a to thus secure the disc D.
The conventional spindle motor generates a rotating magnetic field when an electric current is supplied to the coil 21b, and thus the magnet 23b, that is, the rotor 23 rotates by an electromagnetic force 23b is formed between the coil 21b and the magnet 23b, to thus enable the disc D mounted on the rotor yoke 23a to rotate.
The conventional spindle motor is configured to have a predetermined gap (or space) between the bottom of the sleeve bearing 17 and the slit washers 14 so that oil smoothly passes between the sleeve bearing 17 and the slit washers 14 at the time when the sleeve bearing 17 is press-fitted into the bearing housing 13, taking the oil circulation path between the sleeve bearing 17 and the rotating shaft 19 into consideration.
Referring to FIG. 3, the oil circulation path of the conventional spindle motor will be described below. First, oil rises up along between the sleeve bearings 17 and the rotating shaft 19, and then moves to the outside of the sleeve bearing 17 along between the upper end of the sleeve bearing 17 and the oil shatter-proof washer 20. Sequentially, oil continues to flow down along the recess 17a of the sleeve bearing 17, and then moves toward the bottom of the rotating shaft 19, along a space S formed between the slit washers 14 and the bottom of the sleeve bearing 17.
However, in order to prepare the predetermined space S through which oil passes between the bottom of the sleeve bearing 17 and the slit washers 14, a press-fitting force is appropriately controlled when the sleeve bearings 17 is press-fitted into the bearing housing 13, lest the sleeve bearing 17 should be fully in contact with the slit washers 14.
Accordingly, when the sleeve bearing 17 is press-fitted into the bearing housing 13, the press-fitting force and direction have a huge impact on verticality and wobble. In other words, since the rotating shaft 19 that is inserted into and coupled with the sleeve bearing 17 is not vertical unless the sleeve bearing 17 is vertically assembled with the bearing housing 13, the rotating shaft 19 may be eccentrically rotated to thus cause vibration and noise to occur.
Moreover, when the sleeve bearing 17 is press-fitted into the bearing housing 13, an inner diameter portion of the sleeve bearing 17 may change by the press-fitting force. As a result, in order to correct the change in the inner diameter portion of the sleeve bearing 17, machining of the inner diameter portion of the sleeve bearing 17 is required by a sizing process.
In addition, when a spinning or coking process is executed in order to perform a bonding process between the bearing housing 13 and each of the base plate 11 and the cap 15, a verticality of the bearing housing 13 with respect to the base plate 11 will occur. As a result, when the sleeve bearing 17 is press-fitted into the bearing housing 13, a run-out problem from the verticality of the sleeve bearing 17 may occur to accordingly require a repair the run-out problem. In this case, if the rotating shaft 19 is assembled with the bearing 17 without repairing, the rotating shaft 19 is tilted from the base plate 11, and thus vibration and noise may occur.
In addition, when a spinning or caulking process of joining the cap 15 to the bearing housing 13 is poor, oil of the sleeve bearing 17 may leak through a contact area between the bearing housing 13 and the cap 15.
In addition, since the coupling between the bearing housing 13 and the base plate 11 and the coupling between the bearing housing 13 and the cap 15 are accomplished by a spinning or caulking process of the outer and inner projections 13a and 13b, an assembly process becomes complicated.